Wheels for automobiles are typically attached to a wheel hub by a plurality of threaded studs and a plurality of mating lug nuts. The threaded studs are equally spaced around a bolt circle on a wheel hub, and outwardly extend from the wheel hub. Large automobiles typically include five wheel studs. The tire rim of a mating wheel includes a plurality of spaced mounting holes that align with the spaced studs on the wheel hub. The wheel is mounted on the hub by placing the tire rim over the spaced studs such that a stud outwardly extends through each mounting hole, threadibly engaging a mating lug nut on each stud, and tightening each lug nut to a prescribed torque value. The portion of the wheel rim around each mounting hole is typically conically shaped, and receives a matching conical seating end of a mating lug nut. When the lug nuts are seated and tightened, the conical portions of the rims and the lug nuts cooperate to center the rim on the studs and the wheel hub.
With some modifications, wheels, rims, studs and lug nuts like those described above are used for certain types of racing cars, including racing cars like those used in stock car races sanctioned by NASCAR®. An example of a typical wheel assembly 10 of a typical American stock car is shown in FIGS. 1 and 2. As shown in FIG. 1, a tire 9 mounted on a rim 12 is mounted over five equally-spaced wheel studs 14, and is secured by five lug nuts 16 threadibly engaged on the studs (14). As shown in FIG. 2, an inner end 15 of each stud 14 is fixed to a wheel hub 20. The stud 14 includes a threaded portion 27 that outwardly extends from the hub 20, and is received through an aligned hole 11 in the tire rim 12. The rim 12 includes a conical seat 13 around each mounting hole 11. A lug nut 16 having a conical seating end 13 and an opposed outer end 23 is threadibly engaged on the threaded portion 27 of the stud 14. Each lug nut includes a threaded bore 29 and a plurality of hexagonally arranged external flats 25 for engagement with a torquing tool. Each of the lug nuts 16 is tightened to a prescribed torque value that provides a tensile preload in each stud 14 that is sufficient to retain the wheel 10 on the hub 20 under anticipated driving conditions. As shown in FIG. 2, when a lug nut 16 is engaged on a mating stud 14 and is fully seated in the conical portion 13 of the rim 12, a first or outermost male thread 19 on the stud 14 outwardly extends beyond the outer end 23 of the lug nut 23.
During a race, a car's tires 10 must be periodically changed due to tire wear or tire damage. In order to minimize the time required to change a race car's tires 10 during a race, race crews have developed a special method for installing a new tire and wheel assembly 10 onto a wheel hub 20. First, each wheel stud 14 includes a non-threaded extension 18 that outwardly extends well beyond the threaded portion 27 of each stud 14. In addition, before a race, a lug nut 16 is centered within each conical recess 13 of each wheel rim 12 of each replacement tire 10, and the lug nuts 16 are glued to the rim with a temporary adhesive. During an in-race tire change, once an old tire has been removed, a new tire 10 with the adhered lug nuts 16 is placed over the extensions 18 on each stud 14. As shown in FIG. 2, the extensions can include a tapered or bullet-shaped tip 17 for use in guiding the rim 12 over the studs 14. When a first lug nut 16 is seated and tightened using a powered torque wrench, the rim 12 is drawn tight up against the wheel hub 20. As the rim 12 is drawn against the hub 20, contact between the other untightened lug nuts 16 and the first threads 19 on their respective mating studs 14 causes the other glued-on lug nuts 16 to separate from the rim. Once separated, the untightened lug nuts 16 are suspended in place by the wheel stud extensions 18 until they are individually seated and torqued. Accordingly, by gluing the lug nuts 14 to the rims 12 and by providing wheel stud extensions 18 to capture the lug nuts 14 once separated, the need to individually position each lug nut 16 over a mating stud 14 is eliminated, and valuable time can be saved.
On occasion, it is possible that a lug nut 16 is not fully engaged or fully tightened onto its mating stud 14 during a pit stop. During a race, even a single loose lug nut 16 can present several problems. First, a partially secured tire 10 can cause unwanted vibration that can affect a race car's handling and performance. Second, and most importantly, even a single loose lug nut 16 can cause a partially secured tire 10 to break free from its hub 20, thereby creating a substantial danger to the car's driver, other drivers, race crews, race officials, and other bystanders, including race spectators. Because stock cars can reach speeds of up to about 200 miles per hour, a loose tire can become a dangerous projectile. Accordingly, racing rules prohibit cars from racing with one or more loose lug nuts, and race officials are assigned to observe tire changes and to inspect cars for loose lug nuts before the cars return to the racetrack. If a race official observes a loose lug nut on a car as the car leaves the pit, the official will order the car to immediately return to the pit to correct the problem. One method for visually confirming that a lug nut 16 is fully engaged on the threaded portion 27 of a stud 14 is to confirm that at least the first thread 19 of the stud 14 is visible beyond the outer end 23 of the nut 16. Though such a method cannot absolutely confirm that a lug nut 16 is fully tightened onto a mating wheel stud 14, the method does provide verification that all of the internal threads 29 of the lug nut 16 are engaged with the external threads 27 of the stud 14, and that the lug nut 16 is very likely to be fully seated against a tire's rim 12.
Unfortunately, it can be very difficult to visually detect a loose lug nut 16 during a race. In particular, it can be very difficult to detect a loose lug nut 16 after a tire change, and before a car leaves the pit and returns to the racetrack. Because all four tires can be changed by an expert pit crew in less than fifteen seconds, there is very little time for a crew member or race official to visually inspect all twenty of car's lug nuts 6 before the car returns to the racetrack. In addition, an inspecting race official or crew member may be a substantial distance away or at a less than ideal position, thus making it difficult to visually detect that one or more lug nuts is loose on one or more tires. Accordingly, there is a need for an improved lug nut that can provide a reliable and readily visible indication that a lug nut has been fully engaged onto the threads of a mating wheel stud, and that a race car can safely return to racing.